Re: cost of CREATE VIEW ... AS SELECT DISTINCT - Mailing list pgsql-sql

On Tue, Mar 29, 2005 at 11:07:20 +0100, T E Schmitz <mailreg@numerixtechnology.de> wrote:
> 
> Would the "SELECT DISTINCT origin" always cause a sequential table scan 
> regardless whether there is an index on the origin column or not?

It's worse than that, SELECT DISTINCT cannot use a hash aggregate plan
and will need to do a sort to eliminate duplicates. Unless the view
is used in a way that restricts the candidate rows, this probably isn't going
to be very fast. You might be better off changing the view to use GROUP BY
instead of DISTINCT.